Remove deployment_notes.md
Remove deployment_notes.md

The information in this file is very out of date, and from what I can
see mostly irrelevant now.

- This was written when we were using xapain as our search backend, but
  we not use Elasticsearch, so that blocker for N > 1 server deploys has
  now been removed
- Mapit is no longer pinned at the branch mentioned
- There doesn't seem to be any mentions of robots.txt in
  http.conf-example

mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola,mysociety/pombola